1. Field of the Invention
The present invention relates to a recirculating sheet feeder which is preferably used in, for example, a recirculating document feeder of a copying machine, and capable of feeding a stack of sheets such as a document or the like, seriatim, from top of the stack to a reading station, and returning the sheet to the bottom of the stack, and at the same time, detecting completion of the feeding of the sheets.
2. Description of the Prior Art
In recent years, in an electrostatic copying machine, there is a trend to provide a recirculating document feeder which conveys plural document sheets seriatim to a reading station automatically for optical scanning of the documents, and executes reading and exposing operation of a document image.
The document sheets to be copied are contained in stack in a document container of the document feeder. When the copying operation is started, the document is fed, seriatim automatically from the document container and conveyed to a document transporting path provided with the reading station. In a conventional recirculating document feeder, the document completing a presenting operation of the document image of the reading station is returned to the document container, and received therein separately from the documents which are still not fed. In order to copy one set automatically for plural document sheets, detecting means for detecting the state, wherein all of the document sheets contained in stack in the document container are fed to the document transporting path for the reading and exposing operation is necessitated, toward this end, a detecting device for detecting the aforementioned state is provided.
FIG. 1 is a schematic sectional view showing a first conventional example. The detecting device 1, for detecting completion of feeding the documents, is disposed in the vicinity of a document container 5 in which plural document sheets are contained in stack. The detecting device 1 is constituted by including a detecting unit 2 consisting of a light emitting element and a light receiving element integrated with each other, and an actuating member 4 provided at a portion with a mirror 3 which reflects light from the detecting unit 2. That is the light emitting element of the detecting unit 2 emits light to the actuating member 4 disposed beneath the detecting unit 2 in FIG. 1. This light is reflected by the mirror 3 of the actuating member 4, and when received by the light receiving element of the detecting unit 2, it is detected that all of the documents d were fed.
When the documents d are received in the document container 5 in stack, the actuating member 4 of the detecting device 1 is arranged under the document at the bottom of the documents d contained in stack. When the copying operation is started, from the document container 5, the documents d contained are fed seriatim from the one on top rightward in FIG. 1. When the reading and exposing operation for the document fed is completed, the document taken out is returned to the document container 5 from the under side. At this time, the document being received is returned by inserting the downstream end in the receiving direction underneath the actuating member 4.
When the stack of documents d are fed seriatim from the one on top from the document container 5, and received seriatim in the bottom again in such a way, associated with such feeding and returning operation, the actuating member 4 is gradually pushed upward of the figure. Light emitted downward of the figure from the detecting unit 2 is interrupted by the document d when it is not fed and remained on the actuating member 4. When feeding of the documents d proceeds and the last document is fed, the mirror 3 of the actuating member 4 is exposed against the detecting unit 2, thereby light is reflected to the detecting unit 2 to detect completion of feeding one set of plural document sheets d.
In this first conventional example, as the detecting device 1, the detecting unit 2 including the light emitting element and the light receiving element must be installed in a spaced relation at an opposing position, when the document d contained in the document container 5 is not present on the actuating member 4. Accordingly, the number of component parts increases and a space occupied for detecting the document feeding state becomes larger to deteriorate the utilization efficiency of space.
FIG. 2 is a schematic sectional view showing a second conventional example. The actuating member 4 is pivoted rotatably on a machine body 9, and at one end 4b thereof, a spring 7 is fixed between the machine body 9 to urge the other end 4a contacted to the document d contained in the document container 5 from the underside upward. In the vicinity of the actuating member 4, a light receiving element 8 which receives light from a light emitting element, not shown, disposed perpendicularly above the paper surface of FIG. 2 is installed on the machine body 9.
When the documents d are contained in the document container 5 in stack, the other end 4a of the actuating member 4 contacts to the document positioned at the bottom of the documents d received from the underside. As same as the first conventional example, the documents d are fed seriatim from the one on top from the document container 5, and when it is returned to the bottom, the downstream end portion in the receiving direction of the document returned is inserted underneath the other end 4a of the actuating member 4. Thereby, associated with the feeding and returning operation of the document d, the other end 4a of the actuating member 4 displaces gradually upward by the spring 7, accordingly, one end 4b of the actuating member 4 displaces in the opposite direction of the other end 4a. When all of the documents divided by the actuating member 4 and contained in the document container 5 without being fed are fed, a path of light received by the light receiving element 8 from the light emitting element is interrupted by one end 4b of the actuating member 4, thereby detecting feeding of all of the documents d.
In this second conventional example, when the weight of the documents d is light, or the number of document sheets which are divided by the actuating member 4 and not fed decreases, the other end 4a of the actuating member 4 tends to push up the documents not fed and displace angularly by the force of the spring 7, thereby such a situation may occur that one end 4b of the actuating member 4 interrupts the light path of the light receiving element 8. In this case, the detecting signal indicating that all of the documents d were fed is emitted in spite of the documents d being not fed all, thereby causing malfunction.
FIG. 3 is a view showing a third conventional example disclosed in U.S. Pat. No. 4,639,126, and FIG. 4 is a view illustrating its operation. A follow-up-finger which moves as following a document stack 59, which is fed for copying, from the under side is constituted by including a light and small coil spring 80, and its tip is provided with a plug 81 consisting of a synthetic resin. The spring 80 is installed on a member 82 consisting of a synthetic resin and disposed rotatably about an axis of a shaft 83. A second coil spring 84 is also mounted to the member 82, and a weight 85 consisting of a metallic material is provided at one end thereof. The springs 80 and 84 are disposed at an angular relation-ship of 90.degree. or more.
To a plunger of a solenoid 87, a first link 88 is connected by a pin, and to the first link 88 a second link 89 is connected by a pin. The member 82 is pivoted on the second link 89 by the shaft 83, and the second link 89 is installed on a mounting shaft 60 provided on the machine body so as to be able to displace angularly.
Referring to FIG. 4, as long as, at least, a sheet of document is present on the spring 80, the follow-up finger is retained at a position shown in FIG. 4 (2), and the spring 80 is extended substantially horizontally under the document. While, as shown in FIG. 4(3), when the last document is taken out, the weight 85 acts on the member 82 and the springs 80, 84 displace angularly about the shaft 83 by gravity of the weight 85. At a position shown in FIG. 4(3), the springs 80, 84 are both extended in a direction of about 45.degree. from a level. Associated with a sensor 86, the spring 80 is stopped and the follow-up finger is retained at a position shown in FIG. 4(3).
By movement from the position of FIG. 4(2) to that of FIG. 4(3), the spring 80 passes through the front of the sensor 86 and the signal indicating that the last document has been fed for copying from the document stack 59 is sent.
After the last sheet of document stack 59 is returned to a tray, the solenoid 87 is excited. By operation of the solenoid 87, the spring 80 is reset under the last sheet of the document stack 59 as shown in FIG. 4(4).
The solenoid 87 is excited for a short period of about 500 m sec., and during this period, the link 88 is pushed upward and retained. To the upper end of the link 88, the second link 89 is coupled so as to be able to displace angularly. As the link 88 moves upward, the link 89 displaces angularly about the mounting shaft 60. By this angular displacement, the link 89 moves to a substantially horizontal position as shown in FIG. 4(4). At this position, by the operation of the weight 85, the spring 84 moves to a substantially horizontal position, and the spring 80 moves to a substantially vertical position.
As shown in FIG. 4(4), the spring 80 is balanced at the position where its plug 81 directs downward so as to be inserted under the document stack 59. Next, when the solenoid 87 is deenergized, the link 88 moves in a substantially vertical direction and the link 89 is brought to a substantially vertical position, and as shown in FIG. 4(1), by the operation of the weight 85, the member 82 rotates so as to insert the spring 80 under the document stack 59. Thereby, the document stack 59 can be circulated for copying.
In the third conventional example, since the links 88, 89, solenoid 87 and further the sensor 86 are provided to detect one circulation of the document stack 59, the number of component parts is increased by a complicated link mechanism, results in a high cost. Also, as the weight 85 provided on one end of the spring 84 is heavy, in case a sheet of document in the document stack 59 is relatively light, the plug 81 installed on the tip of the spring 80 may push up a few documents remained without being fed and detected by the sensor 86, thus detection of completion of feeding may be led to malfunction.
As such, according to the first conventional example, the space utilization efficiency is deteriorated by the detecting unit 2, and according to the second conventional example, completion of feeding may be detected improperly for the lightweight documents, and further, according to the third conventional example, improper detection for the lightweight documents is apt to occur, besides the number of component parts for detection becomes larger to result in a high cost.
In the recirculating document feeder aforementioned, a circulation path which returns to a document container again from the document container via a reading station is formed, and documents are fed such that, for example, the document on top of the documents stacked on the document container is fed seriatim and returned to the document container at the bottom of the stacked documents.
As a configuration for realizing the feeding operation of the documents above-mentioned, it may be considered, for example, to provide a vacuum suction unit and a conveying belt integrated with each other, on the upper side of a stack of documents. That is, a sheet of document on top of the document stack is sucked onto the peripheral surface of the belt by the vacuum suction unit, and fed by driving the belt in this state.
In such a feeder, multiple feeding of the documents which feeds a plural sheets of document at the same time is apt to occur, thus detecting one circulation of feeding and returning the document is unstable.
Besides, when the document fed is returned between the stack of documents and placing member where on the stack of documents is placed, the document being returned may be damaged.